Single pole, double throw, crystal diode switch



p 7, 1968 YUTAKA HORIGUCHI ET AL 3,402,369

SINGLE POLE, DOUBLE THROW, CRYSTAL DIODE SWITCH Filed Oct. 17, 1966 (DA/7790A VOLT/46E 501/1965 ATTEM/4770/V/a3) cow-e04 United States Patent 3,402,369 SINGLE POLE, DOUBLE THROW, CRYSTAL DIODE SWITCH Yutaka Horiguchi and Akio Saeki, Tokyo, Japan, assignors to Nippon Electric Company, Limited, Tokyo, Japan, a corporation of Japan Filed Oct. 17, 1966, Ser. No. 587,128 Claims priority, application Japan, Oct. 19, 1965, ill/64,097, 40/6 1,098 5 Claims. (Cl. 333-7) ABSTRACT OF THE DISCLOSURE A single pole double throw type microwave switching device having a switching time of less than one nanosecond and including a generally Y-shaped rectangular waveguide having one arm as the input and the other two arms as the output, a coaxial waveguide extending perpendicular to the plane of said rectangular waveguide with its axial conductor passing through said rectangular waveguide generally at the center of the Y, a member of dielectric material having an asymmetrical configuration with respect to the direction of an incoming microwave fed into the input arm, a diode mounted in the central region of said Y-shaped rectangular waveguide and connected to said axial conductor, and said diode receiving a biasing voltage for controlling the microwave output in said output arms.

This invention relates to a microwave device, and more particularly to a microwave switching device of the single pole double throw type which is usable as microwave switching means, pulse modulating means, or a principal element of a phase shift keying modulator.

Inasmuch as the device of this invention is classified as a microwave switching device when viewed from its structure and basic operation, the following description, for the purpose of simplicity, will be directed mainly to the switching device embodiment of the invention.

Among the conventional switching devices of the kind used as a principal constituent of measuring equipment for phase or amplitude characteristics, as a phase or amplitude modulator, or as switching means for a communication network, there have been three fundamental proposals.

The first of these includes a mechanical means for switching the transmission path of the microwave power. The second one employs a three terminal ferrite circulator, which is provided by applying to a waveguide circuit the principle described in the article, Pulse-Operated Circulator Switch, by L. Freiberg appearing on page 266 of IRE Transactions on Microwave Theory and Technique, May 1961. By reversing the magnetic field applied to the ferrite element of the device, the direciton of trans mission can be reversed to attain single pole double throw switching operation. The third one is composed of a combination of a plurality of single pole single throw switches which include crystal diodes as control elements, as illustrated in FIG. 2 of Driving the Diode Switch? by N. H. Goldich in Microwaves, August 1965.

When the switching time is required to be extremely short as in the case of pulse modulation, the abovementioned first means cannot be relied on because it includes the mechanical elements. Also, the second means has too long a switching time to be used as the high speed modulating means because the electric current flowing through the magnetizing coil must be reversed each time the switching is performed. Similarly, the third means not only has the difiiculty that the time constant of the circuit as a whole inevitably becomes long because of the 3,402,369 Patented Sept. 17, 1968 use of the number of crystal diodes necessary, but also has the disadvantage that the structure cannot be sim plified.

Accordingly, it is an object of this invention to provide a microwave switching device of simple structure which is substantially free from the above-mentioned difficulties of conventional devices.

Another object is to provide such a simple structure device which has a waveguide branch and only one crystal diode.

All of the objects, feaures and advantage of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of the invention taken in conjunction with the accompanying drawings in which:

FIG. 1 is a perspective view of an embodiment of the present invention, with a portion cut away,

FIG. 2 is a graph showing characteristic curves useful in explaining the performance of the embodiment of FIG. 1, and

FIG. 3 is a perspective view similar to FIG. 1, of another embodiment of the present invention.

The microwave switching device of the present invention preferably comprises a waveguide branch which has Y-shaped arms within the plane of the magnetic field of the electromagnetic wave propagating therethrough, a circular coaxial waveguide which is mounted at the center of the Y-shaped branch piercing through the upper and lower waveguide walls perpendicularly to the magnetic field plane and the outside end of which is shorted by means of a conductor, a member of dielectric or externally magnetized ferromagnetic material which has an asymmetrical configuration with respect to the direction of the incoming microwave propagation and has asymmetrical influence on the microwave propagation and which is disposed within the coaxial waveguide in the vicinity of the Y-shaped branch, a crystal diode mounted in the neighborhood of the dielectric or ferromagnetic material member in such a manner that its positive electrode and negative electrode may be connected to the center conductor of said circular coaxial waveguide, respectively, and a voltage source for supplying a biasing voltage to the crystal diode. One of the arms serves as an inptu means for the incoming electromagnetic wave. The output is derived from either of the other two arms in response to the biasing voltage applied to the diode.

As will be understood from this structure, the device of the present invention can be used as a single pole double throw microwave switching means. Because of its extremely short switching time, the device may also be used as a pulse modulator or as a principal part of a phase shift keying modulator, as will be further referred to later herein.

Referring to FIG. 1, three arms A, B, and C of a rectangular waveguide 1 forms a Y-shaped waveguide branch within the plane of the magnetic field of the electromagnetic wave supplied from a microwave source, not shown, to the arm A. A coaxial waveguide, having a cylindrical outer conductor 2 and an axial conductor 3 disposed along the axis thereof, is rigidly fixed to the Y-shaped waveguide branch. This coaxial waveguide extends through the walls of the Y-shaped branch and is mounted perpendicular to said walls. The outer conductor 2. of the coaxial waveguide is removed within the region enclosed by the waveguide 1, and one end of the coaxial waveguide is shorted by a slidable shorting member 4.

In the portion of the axial conductor 3 of the coaxial waveguide enclosed by the waveguide 1, a crystal diode 5 is inserted in series with the conductor 3. Also, a piece 9 of dielectric material is disposed in surrounding relationship about the axial conductor 3. The diode 5 is disposed in such a vertical position that it may be seen in the vertical and horizontal center when viewed from the input arm A. As a practical matter, the lower end surface of the dielectric material piece 9 is a few millimeters higher than the plane which includes the internal surface of the upper wall of the waveguide 1. Consequently, the dielectric piece 9 cannot be seen from the arm A. The end 7 of the coaxial waveguide is connected to a control voltage source 6 which produces predetermined voltages necessary for the desired switching operation. The lower end portion of the diode 5 is effectively shorted in the operating microwave frequency region by a capacitor 8 having a small capacity, with a view to providing a completely reflective terminal, thereby preventing the incoming microwave energy from leaking out to the circuit of the voltage source 6. The capacitor 8 may be dispensed with if the leaking microwave power is negligible.

The dielectric material piece 9 has a substantially cylindrical configuration with a portion thereof 9a cut out in the axial direction, and is disposed with the cut out surface asymmetrically directed to the arm A. The diameter of the dielectric material piece 9 is determined so that the electromagnetic waves of the TE mode can be transmitted, which is a higher order mode than the fundamental TEM mode for the coaxial waveguide.

Within the coaxial waveguide of the structure described above, the distribution of the field intensity of the electromagnetic wave is dependent on the dimensions, position, and asymmetry of the dielectric material piece 9, the position of the slidable shorting means 4, and the biasing voltage supplied to the diode 5. So far as symmetry of the transmission path concerning the incoming microwave is maintained, the incoming microwave power will be divided into two equal portions, which varies dependently on the biasing voltage. With the device of FIG. 1, however, the incoming microwave is divided into two unequal portions derived from the two output arms, because of the asymmetry of the coaxial waveguide and the higher mode of electromagnetic wave generated, and also because of the unbalanced impedances brought about by the coaxial waveguide which includes the crystal diode on the output arms B and C.

In FIG. 2, in which the biasing voltage V is taken at the abscissa and the relative attenuation db is taken at the ordinate, there are shown two curves B and C of experimental results, which are obtained at 11000 rnHZ. by plotting the output power at the output end of each of the arms B and C with relation to the variation of the biasing voltage supplied to the diode. In these experiments, the dimensions and constants of various parts of the embodiment of FIG. 1 are as follows:

Y-shaped waveguide 1: a symmetrical Y-shaped waveguide of RG52/U (U.S. Army and Navy Standards) having arms B and C forming 120 with each other.

Coaxial waveguide: inner diameter of the external conductor12 mm.; outer diameter of the axial conductor-4 mm.

Crystal diode 5: silver-bonded diode GSB2 sold by Nippon Electric Company, Limited, of Japan. This diode is placed in the center of the Y-shaped branch both in the horizontal and vertical directions.

Dielectric material piece 9: made of Stycast, sold by Emerson & Cuming, Inc., Canton, Mass, and having a dielectric constant of 10. The cylindrical configuration has an outer diameter of 12 mm., an inner diameter of 4 mm., and a length of mm. The side surface of the piece 9 is cut away by a maximum thickness of 1 mm. along the axis thereof. The dielectric piece 9 is placed within the waveguide with the cut-away surface 9a forming an angle of with the direction of propagation of the incoming microwave. The lower end surface of the dielectric piece 9 is fixed at a position a few millimeters higher than the plane including the inner surface of the upper wall of the Y-shap wav g ide.

Shorting member 4: this member is positioned at a point about 20 mm. away from the plane which includes the upper surface of the dielectric piece 9.

The single pole double throw switching characteristics of the device can be changed by adjusting the orientation of the cut-away surface 9a of the dielectric material piece 9 and the position of the slidable shorting member 4.

Among the measured characteristics of the device, the insertion loss is 3.5 db, and the isolation is 15 db, which are not particularly improved compared with such characteristics of conventional devices of this type. However, it should be noted that the switching time is less than 1 nanosecond; such a short switching time cannot be obtained by the conventional devices. This is the reason why the improved device of this invention is applicable to the pulse modulator mentioned above. In other words, the voltage source 6 may be the usual direct current voltage source or a time-division multiplexed pulse signal source, such as that of a PCM or 21 PPM signal source.

Referring to FIG. 3 in which another embodiment of the present invention is shown, and in which the elements corresponding to those of FIG. 1 are denoted by corresponding numerals, the dielectric material piece 9 of the first embodiment is replaced by a piece 19 of ferromagnetic material having similar configuration. In order to suitably magnetize the ferromagnetic material piece 19 in the axial direction, a hollow cylindrical magnetizing coil 19a is disposed surrounding the external conductor 2 of the coaxial waveguide. An energizing current is supplied to the magnetizing coil 19a from a source, not shown. A hollow cylindrical permanent magnet may be used instead of the magnetizing coil 19a.

As the ferromagnetic material piece 19, a Mn-Mg-Al ferrite having a saturation magnetization of approximate 1y 750 gauss and a dielectric constant of 11 may be used. Our experiments indicate that a favorable magnetizing field was approximately gauss. In an operation observed at 11000 mHz., the insertion loss and the isolation were 2 db and 25 db, respectively.

The embodiment of FIG. 3 is superior to the embodiment of FIG. 1 in that the nonreciprocity of the ferromagnetic material contributes to the asymmetry or unbalance of the impedance, in addition to its contribution as a dielectric material, and consequently the insertion loss and isolation characteristics are further improved. In other words, the device of FIG. 3 bears the characteristics of a circulator, which is changeable in response to the magnetizing field, the dimensions of the ferrite piece, and the impedance caused by the crystal diode.

Substantially the same characteristic curves as are shown in FIG. 2 were obtained by our experiments for which the pertinent dimensions and constants are as follows:

Ferromagnetic material piece 19: made of Mn-Mg-Al ferrite having a dielectric constrant of 11. The cylindrical configuration had an outer diameter of 12 mm., an inner diameter of 4 mm., and a length of 8 mm. The side surface of the piece 19 is cut away by a maximum thickness of 0.5 mm. along the axis thereof and is placed within the waveguide with the cut-away surface forming an angle of approximately with the direction of propagation of the incoming microwave. The lower end surface of the cylinder is laid in the plane of the inner surface of the upper wall of the waveguide.

Shorting member 4: the lower end surface of the member is in direct contact with the upper end surface of the ferromagnetic piece 19.

The magnetizing coil 19a: energized by an energizing current such that a magnetic field of 130 gauss will be produced along the axis of the ferromagnetic piece 19.

Other constituent parts are identical to those in the embodiment of FIG. 1.

As is well known to those knowledgeable in this art, a single pole double throw switch device can be used as a phase shift keying modulator in which one of the two output arms is directly coupled to one of the two inputs of a hybrid and the other of the output arms is coupled to the other of the two inputs through a phase shift means, and in which the incoming microwave is phase shift keyed when viewed at the output side of the hybrid, depending on whether it has been caused to pass through the route of said one arm or the other in response to the switchcontrol voltage. Inasmuch as the switching time of the present device is extremely short, the invention is particularly well suited to modulators of this kind whereby remarkable improvement in structure and performance are achieved.

Although the invention has been described above in connection with two embodiments and their several modifications and applications, it should be understood that these are merely exemplary and that various further modifications are possible. For example, the coaxial waveguide may be fixed at a point other than the center of the Y- shaped branch. Also, different angles between the Y- shaped arms may be suitably employed. Furthermore, the dimensions of the constituent parts of the device are not restricted to the specific examples described above, but can be modified therefrom. Still other variations within the scope of this invention will occur to those skilled in the art and accordingly the invention is to be limited only in accordance with the scope of the appended claims.

What is claimed is:

1. A microwave device comprising a substantially Y-shaped portion of rectangular waveguide having its three arms within a plane generally parallel to the plane of the magnetic field of an incoming microwave propagating therethrough,

one of said arms serving as the input for the incoming microwave and the other two of the arms serving as the output means for said microwave,

a coaxial waveguide having an outer conductor and an axial conductor each extending in the direction perpendicular to said plane,

said outer conductor being fixed at a point intermediate its ends at approximately the central part of said Y- shaped portion with said axial conductor passing through said rectangular waveguide,

a crystal diode disposed within the region enclosed by the rectangular waveguide and disposed in conductive relation with said axial conductor,

a member of selected dielectric material disposed within said coaxial waveguide surrounding said axial conductor,

said material member having an asymmetrical configuration with respect to the direction of propagation of said incoming microwave,

a slidable shorting means disposed on the one end of said coaxial waveguide for providing a short circuit between the outer conductor and the axial conductor,

and a control voltage source connected to the other end of said coaxial waveguide for supplying control voltages to said diode, whereby the incoming microwave is led to either of the other two arms of said Y-shaped portion in response to said control voltage.

2. The invention described in claim: 1 wherein said selected dielectric material member comprises a piece of ferrite and wherein a means is provided for suitably magnetizing said ferrite piece in the direction of said coaxial waveguide.

3. The invention described in claim 2 wherein said ferrite material comprises manganese, magnesium and aluminum.

4. The invention described in claim 2 wherein said magnetizing means comprises a magnetizing coil surrounding said coaxial waveguide.

5. The invention described in claim 2 wherein said magnetizing means comprises a hollow, cylindrical permanent magnet surrounding said coaxial waveguide.

References Cited UNITED STATES PATENTS 3,299,372 1/1967 Saeki et al.

HERMAN KARL SAALBACH, Primary Examiner.

PAUL L. GENSLER, Assistant Examiner. 

